I've been a mother all of my adult life (since I was 18). My baby will be grown in less than 4 years. Life will definitely change for me. I don't remember what it's like to focus on myself. I might have to steal a grandbaby.
Stealing grandbabies does help.
I 'empty nested' 3 years in a row, got a break for a year then the final went. A few years later I pushed out the X but she ended up getting everything because I was stooopid and hired a worthless lawyer.
I went from a full family of six to zip in a handfull of years.
Empty nest can be brutal alone. There are tricks that help like playing a radio in their room. The feeling will pass but you're right, it is a big life change.
Its hard not to smother them if you stay close by them but if they are going away to school or the service it can get over-powering at times.
Hobbies help alot.